1. Field of the Invention
The present invention relates to an energy trap type piezoelectric resonance component which is applied to a piezo-resonator, a piezoelectric filter or the like, and more particularly, it relates to an energy trap type piezoelectric resonance component utilizing a shear vibration mode such as a thickness shear vibration mode or a width shear vibration mode.
2. Description of the Background Art
FIG. 2 is a perspective view showing an example of a conventional energy trap type piezo-resonator 1 utilizing a thickness shear vibration mode. This piezo-resonator 1 comprises an elongated rectangular piezoelectric substrate 2 and electrodes 3 and 4 which are formed on both major surfaces thereof. The piezoelectric substrate 2 is polarized along arrow P. The electrodes 3 and 4 are formed to be opposed to each other in a back-to-back manner through the piezoelectric substrate 2 on a central region thereof, so that vibration is excited by the portion opposing the electrodes 3 and 4 to each other. Further, the electrodes 3 and 4 are formed to reach different end portions of the piezoelectric substrate 2 respectively, so that the piezo-resonator 1 can be electrically connected with an external member and mechanically held on both ends of the piezoelectric substrate 2.
In the aforementioned energy trap type piezo-resonator 1, the as-excited vibration is trapped in the portion opposing the electrodes 3 and 4 to each other, i.e., in a vibrating part, so that the vibration is sufficiently damped around both ends of the piezoelectric substrate 2. Even if the piezo-resonator 1 is mechanically held at both ends of the piezoelectric substrate 2, therefore, its resonance characteristic is hardly deteriorated.
Such piezo-resonators 1 are generally mass-produced by forming mother electrodes on both major surfaces of a mother piezoelectric substrate and thereafter cutting the mother piezoelectric substrate along its thickness. In order to increase the number of such piezo-resonators 1 which can be obtained from the mother piezoelectric substrate for improving mass productivity, it is desirable to reduce the length L of each piezoelectric substrate 2. Further, miniaturization is required for the piezo-resonator 1 similarly to other electronic components, and hence it is desirable to reduce the length L of the piezoelectric substrate 2, in order to satisfy such a requirement.
When the length L of the piezoelectric substrate 2 is reduced, however, the vibration is insufficiently damped around both ends of the piezoelectric substrate 2. When both ends of the piezoelectric substrate 2 are mechanically held, therefore, the resonance characteristic is disadvantageously deteriorated. In particular, the resonance frequency of the piezo-resonator 1 is decided by the thickness of the piezoelectric substrate 2, while the length L of the piezoelectric substrate 2 must be increased in order to obtain a lower frequency by increasing the thickness of the piezoelectric substrate 2. If the length L of the piezoelectric substrate 2 is reduced in this case, it is extremely difficult to form a piezo-resonator having a sufficient resonance characteristic.